1. Field of Invention
Exemplary aspects of the present invention relate to a surface-emitting type semiconductor laser and a method for manufacturing the same.
2. Description of Related Art
A surface emitting semiconductor laser is a semiconductor laser which emits laser light in a direction perpendicular to a semiconductor substrate. Surface emitting type semiconductor lasers have excellent characteristics including, for example, easy handling, low threshold currents, etc., compared to related art edge emitting semiconductor lasers. Thus, this technology may be applied to a variety of sensors and light sources for optical communications. However, the control of polarization planes of a surface-emitting type semiconductor laser is difficult because of the symmetry of its planar structure. Therefore, when a surface-emitting type semiconductor laser is used for an optical system with a polarization dependence, instability of polarization planes causes noise. In this respect, a variety of methods to control polarization planes are proposed as follows.
Japanese laid-open patent application HEI 8-116130 and Japanese laid-open patent application HEI 10-27938 disclose methods to control polarization planes by making a planar configuration of a resonator 140 have an anisotropic shape, such as a rectangular shape, an oval shape, or the like. In this case, only specific modes oscillate because its current density distribution is anisotropic. However, according to these methods, the current density distribution is not uniform, and the energy usage efficiency may be lowered.
Japanese laid-open patent application HEI 6-224515 discloses a method to control polarization planes by adding anisotripic strain to an active layer. In this case, anisotropy appears in its gain, such that only specific modes oscillate. However, according to this method, SiN is formed on the side surface of the resonator 140 at different temperatures in order to add anisotripic strain to the active layer, which complicates the process. Furthermore, according to this method, the planar configuration of the resonator 140 is practically limited to a quadrilateral shape to obtain sufficient effectiveness in controlling polarization planes. A circular planar configuration does not demonstrate effectiveness in controlling polarization planes.
Japanese laid-open patent application HEI 11-307882 discloses a method to control polarization planes by providing an oxide layer for current constriction adjacent to an active layer, and an oxide layer for adding stress (in anisotropic configuration) to thereby add large stress to the active layer while maintaining the energy use efficiency. In this case, the oxide layer structure adjacent to the active layer and oxidation process are complicated, and the service life of the device may be adversely affected.